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Selection for resistance to monensin, nicarbazin, and the monensin plus nicarbazin combination
1Lilly Research Laboratories, A Division of Eli Lilly and Company, Greenfield, Indiana 46140.
Abstract:
Two series of experiments were conducted to assess the relative ability of strains of Eimeria acervulina and Eimeria tenella to develop resistance to monensin (MON), nicarbazin (NIC), and the monensin plus nicarbazin combination (MON plus NIC). The studies were designed so that drug concentrations in the selection experiments were increased whenever possible. During selection, E. acervulina increased its reproductive index in the presence of NIC or MON plus NIC, equivalent selection in the presence of MON resulted in only a slight increase in reproductive ability. Eimeria tenella, however, was unable to increase its reproductive capacity to the respective drugs. Sensitivity tests after 60 generations of selection revealed that patterns of resistance development for E. acervulina and E. tenella corresponded with the changes in reproductive indices established in the selection experiments. Thus, results of these tests indicate that E. acervulina possesses the ability to develop resistance to NIC and MON plus NIC. Under essentially the same conditions of selection, E. tenella developed only partial resistance to the respective drugs.
Insights
Eimeria acervulina developed resistance to nicarbazin and monensin plus nicarbazin, while Eimeria tenella showed only partial resistance to these anticoccidial drugs after 60 generations.
Area of Science:
- Veterinary Parasitology
- Antiparasitic Drug Resistance
- Poultry Health
Background:
- Anticoccidial drugs like monensin and nicarbazin are crucial for controlling Eimeria infections in poultry.
- Understanding the development of drug resistance in Eimeria species is essential for maintaining treatment efficacy.
- Eimeria acervulina and Eimeria tenella are significant poultry pathogens for which resistance is a growing concern.
Purpose of the Study:
- To evaluate the relative ability of Eimeria acervulina and Eimeria tenella to develop resistance to monensin (MON), nicarbazin (NIC), and a combination of MON plus NIC.
- To determine the patterns of drug resistance development in these Eimeria species under prolonged drug exposure.
- To assess the correlation between changes in reproductive indices and acquired drug resistance.
Main Methods:
- Two experimental series involving sequential exposure of Eimeria strains to increasing concentrations of MON, NIC, or MON plus NIC.
- Selection experiments conducted over 60 generations to induce drug resistance.
- Measurement of reproductive indices as an indicator of parasite adaptation and survival.
- Sensitivity tests performed post-selection to quantify the level of resistance developed.
Main Results:
- Eimeria acervulina demonstrated increased reproductive indices in the presence of NIC or MON plus NIC, indicating successful adaptation and resistance development.
- Eimeria tenella showed limited ability to increase its reproductive capacity, suggesting a lower potential for resistance development to the tested drugs.
- Sensitivity tests confirmed that E. acervulina developed resistance to NIC and MON plus NIC, whereas E. tenella exhibited only partial resistance.
Conclusions:
- Eimeria acervulina can develop significant resistance to nicarbazin and the monensin plus nicarbazin combination.
- Eimeria tenella exhibits a lower capacity for developing resistance to these anticoccidial agents under similar selection pressures.
- These findings highlight differential resistance development potential among Eimeria species, impacting strategic drug use in poultry farming.